In a distributed storage system, duplicated data is stored in multiple disk nodes. Thereby, even if a failure occurs in one disk node, system operation can be continued.
However, if the disk node has stopped due to failure, when the data which has been stored in the disk node is updated, only one piece of the duplicated data is updated and the data included in the disk node which has stopped cannot be updated. Consequently, after the disk node which has stopped recovers, the data in the disk node is updated and a duplicated state (redundant configuration) of the data is established. However, in such a case, data redundancy is lost until the disk node in which the failure has occurred is recovered.
In order to maintain the redundant configuration, the data which has been managed by the disk node which has stopped due to the failure needs to be copied to another disk node. Data to be copied can be obtained from a disk node which constitutes the duplication with the disk node which has stopped and manages the same data as the data within the disk node which has stopped.
It should be noted that an amount of data managed by a disk node has become larger in recent years. Thus, it takes a long time to copy all data which has been managed by one disk node. Then, the disk node which has stopped may also be recovered before all data is completely copied. It is inefficient to continuously copy all data also in such a case. Consequently, there is considered a technique in which, among the data which has been managed by the recovered disk node, data which has not been updated during a period of the stop due to the failure is not copied subsequently, and data which is managed by the recovered disk node is set to be valid.